In mobile networks, e.g., according to the 3GPP (3rd Generation Partnership Project), it is known to use relaying for improving capacity and/or coverage of the network. For example, in 3GPP LTE (Long Term Evolution) relaying was introduced in the Release 10 Technical Specifications (TSs). The general idea of relaying is that a relay node (RN) receives a transmission from a sender and forwards this transmission to a recipient. For example, a transmission can be received from a base station, in 3GPP LTE referred to as “evolved Node B” (eNB), and be forwarded to a mobile terminal or other type of user equipment (UE), or vice versa. In 3GPP LTE, a RN communicates with its serving eNB, also referred to as donor eNB, via a backhaul link, and provides access to the UEs attached to a relay cell of the RN via an access link. Both the backhaul link and the access link are implemented using the LTE radio interface.
There are basically two different realizations of RNs. First there are RNs, which can separate access and backhaul links sufficiently well, e.g., by means of separated antennas or by means of separated frequency bands, such that they do not have any restrictions on the radio interface of the access or backhaul link. Second, there are RNs whose access and backhaul links would interfere with each other severely such that those RNs require the configuration of access and backhaul subframes in order to separate the signals in the time domain. In configured backhaul subframes, the RN can communicate with the donor eNB and in access subframes it can communicate with the UEs attached to the relay cell. In downlink (DL) backhaul subframes, in which the RN may receive data from its donor eNB, the RN does not transmit the signals that are provided in regular subframes, such as reference signals, to the attached UEs, i.e., UEs in connected mode or UEs in idle mode. As explained in 3GPP TS 36.216, Section 5.2, the RN declares the backhaul subframes as MBSFN (Multimedia Broadcast/Multicast Services over Single Frequency Network) subframes towards the UEs. This has the purpose of not confusing the attached UEs. Accordingly, there are restrictions concerning the selection of the backhaul subframes. However, as explained in 3GPP TS 36.211, Section 6.7, the RN still provides control information, such as the Physical Downlink Control Channel (PDCCH), the Physical Control Format Indicator Channel (PCFICH), the Physical Hybrid Automatic Repeat Request (HARQ) Indicator Channel (PHICH), and reference symbols in the control region of the subframe, which in MBSFN subframes consists of the first or first and second Orthogonal Frequency Division Multiplexing (OFDM) symbols, see 3GPP TS 36.211, Section 6.7. The PCFICH dynamically provides information about the actual control region size. The remaining OFDM symbols in the MBSFN subframe make up the MBSFN region. In regular subframes, the OFDM symbols not belonging to the control region are referred to as data region.
Since the RN transmits during the control region of the MBSFN subframe, and may therefore not be able to receive control signaling from its donor eNB, a new control channel, i.e., the R-PDCCH was introduced in LTE Release 10 (see 3GPP TS 36.216, Section 5.6.1). This allows the donor eNB to transmit control information in the data region of a subframe to the RN.
In 3GPP LTE, Multimedia Broadcast/Multicast Services (MBMS) are provided for efficient delivery of multicast data or broadcast data. Multicast data are data intended for reception by multiple UEs, and broadcast data can be considered as a specific case of multicast data which are intended for all UEs capable of receiving the multicast data. In the context of MBMS, broadcast data may be received by all connected UEs supporting MBMS, whereas reception of multicast data may be limited to a subgroup of the connected UEs by authentication.
A MBSFN coordinates the transmission of MBMS data, i.e., broadcast data or multicast data, among a group of eNBs such that all involved eNBs jointly transmit the data, i.e., transmit the same data in a synchronized manner using the same time and frequency resources. From a UE perspective all signals combine over the air resulting in an improved signal to interference and noise ratio (SINR). MBMS transmission in MBSFN mode is carried on the Physical Multicast Channel (PMCH) and performed in the MBSFN region of the MBSFN subframe. In LTE Releases 9 and 10, the non-MBSFN region, also referred to as the control region, which consists of the first or first and second OFDM symbols, is used by the eNB to provide cell-specific control information. The size of the control region is semi-statically configured by the Multi-cell/Multicast Coordination Entity (MCE) for all cells participating in an MBSFN area and signaled via PCFICH.
For the PMCH, a constant modulation and coding scheme (MCS) has to be set in all cells of the same MBSFN area. Within an MBSFN area, there is no interference between MBMS transmissions of different cells. This allows to set an MCS with lower robustness than used for unicast at cell borders. MCS with lower robustness may achieve higher data rates and are suitable if the coverage is good throughout the MBSFN area (signal to noise ratio (SNR) above the minimum required for the chosen MCS). If the PMCH MCS robustness is set rather low, more “coverage holes” exist for the PMCH transmission than for unicast transmissions. It would therefore be desirable to improve coverage for MBMS transmission in MBSFN mode, e.g., using relaying. However, according to 3GPP TS 36.300, Section 15.1, RNs do not support MBMS.
Accordingly, there is a need for efficient techniques which allow for efficient delivery of multicast data and broadcast data also when using relaying.